Process for the production of manganese-silicon alloy

ABSTRACT

A PROCESS FOR THE PRODUCTION OF A MANGANESE-SILICIDE ALLOY HAVING A LOW CARBON CONTENT INCLUDING SMELTING MANGANESE ORE, SILICON METAL AND MANGANESE-SILICON SLAG IN AN ELECTRIC FURNACE WITH SUFFICIENT CARBONACEOUS REDUCTANT TO PROVIDE A MELT OF MANGANESE-SILICIDE ALLOW A THROWAWAY SLAG, INTRODUCE THE MELT INTO A LADLE, AND THEN SEP ARATING REMOVING THE ALLOY AND THROW-AWAY SLAG FROM THE LADLE. THE CARBON IS USED AS AN EXCLUSIVE REDUCING AGENT AND THE SILICON IS USED ONLY FOR ALLOYING PURPOSES. IN THE INVENTION, THE THROW-AWAY SLAG CONTAINS MANGANESE VALUES AND IT RECYCLED, THUS MAKING POSSIBLE THE DIRECT USE OF MANGANESE ORE AS THE MANGANESE BEARING MATERIAL.   D R A W I N G

y 1972 l. MADRQNIC ETAL 3,666,438

PROCESS FOR THE PRODUCTION OF MANGANESE-SILICON ALLOY Filed Nov. 16,1970 I P 2 P l m ore ilia l Coal Mn d cow eniidte L 38 W 612 hi ng m I OlGCtT'IC Open Arc smelting Furnace Ladle With Bolt m SICLG Tapping H e lFtidAlltfoy Cast Iron -22 p Poured Pots For Slag 24 26 885 5 |8 SlagDmnplng Slag Crush-L g Cooltmg waste 2 81 3O A a ggi i 2O Crushm o Recycle or pp g To Process r Concentmti 32 S10 34 Plant was I 36 Mn 31Concentrate w INVENTORS IVO MADRONIC ATTORNEYS United States Patent3,666,438 PROCESS FOR THE PRODUCTION OF MANGANESE-SILICON ALLOY lvoMadronic, Marietta, Ohio, and Akgun Mertdogan, Homewood, Ill., assignorsto Interlake, Inc., Chicago,

Filed Nov. 16, 1970, Ser. No. 89,904 Int. Cl. C2211 7/06 US. Cl. 75-10 9Claims ABSTRACT OF THE DISCLOSURE A process for the production of amanganese-silicide alloy having a low carbon content including smeltingmanganese ore, silicon metal and a manganese-silicon slag in an electricfurnace with suflicient carbonaceous reductant to provide a melt ofmanganese-silicide allow and a throwaway slag, introducing the melt intoa ladle, and then separately removing the alloy and throw-away slag fromthe ladle. The carbon is used as an exclusive reducing agent and thesilicon is used only for alloying purposes. In the invention, thethrow-away slag contains manganese values and is recycled, thus makingpossible the direct use of manganese ore as the manganese bearingmaterial.

BACKGROUND OF THE INVENTION This invention relates in general to aprocess for the production of manganese-silicon alloys and moreparticularly relates to the production of a manganese-silicide alloyhaving a low carbon content from manganese ores.

Generally, manganese-silicide alloys have high manganese and siliconcontents and relatively low amounts of carbon and other elementstherein. Such alloys are generally employed as additives, such asdeoxidizers or the like, for the production of low carbon steels.

In the past, manganese-silicide alloys have generally been produced bysmelting manganese ores, quartzite, reducing agents and fluxes in anelectric furnace. Since the specification for manganese-silicide alloysrequires a controlled silicon content and relatively low carbon, theoperation and/or control of the electric furnace to achieve the desiredselective reduction of the charge is of utmost importance and is,therefore, highly critical. Accordingly, variations in the chargematerial analysis, in the electric furnace operation, and in theweighing of the charge and/ or additions thereto, all act to eifect thequality and quantity of the ultimate alloy product produced. Moreover,in the prior art processes, difficulties have been encountered inmaintaining such control conditions, particularly in that an extremelyequilibrated composition, as well as careful regulation of the otheroperating conditions was required. Thus, where such conditions were notproperly maintained, the silicon content in the alloy product varied ina relatively wide range, such as from 25% to 35%. As a result, thequantity of commercial first quality products having a controlledsilicon content of 28% to 32% and a carbon content of .05% maximum waswell below desired requirements.

In addition to the foregoing, such prior art processes Were not entirelysatisfactory for a number of reasons. For example, the alloy was oftensubjected to overheating and/or certain amounts of the principalelements desired (i.e. silicon) were carried away and not used in thealloying. Furthermore, the production costs of such prior processes werehigh, and the average production time for producing a first qualityalloy product were of relatively high duration oftentimes requiringexcessive operating personnel and/or auxiliary equipment. Still further,in such prior processes there were oftentimes produced Patented May 30,1972 SUMMARY OF THE INVENTION The present invention relates to a processfor the production of a manganese-silicon alloy having a low carboncontent comprising, smelting manganese ore and manganese-siliconmaterials having a substantial metallic silicon value with sufiicientcarbonaceous reductant to provide a melt alloy containing high values ofelemental manganese and silicon and a manganese slag, and thenseparating the melt alloy and slag from one another. Preferably, theprocess includes providing a charge comprising manganese ore, coal andslag from the same process and adding suflicient silicon in order tobring the final alloy to the desired silicon level, smelting the chargein a furnace to provide a melt of manganese-silicide alloy and athrow-away slag, introducing the melt into a ladle, and then separatelyremoving the alloy and throw-away slag in.the ladle from one another. Inthe invention, the throw-away slag with a predetermined slag to alloyratio (i.e. in the furnace) may be continuously recycled with a newcharge for reduction in the furnace. In a modified form, predeterminedamounts of the manganese ore, coal, silicon metal and manganese siliconslag from the same process may be blended with a manganese-silicon alloyfor reduction in the furnace.

By the foregoing and following description, it will be seen that thereis provided a novel process for the produc tion of manganese-siliconalloys which reduces the criticality required in furnace operation andin determining the composition and/or-weights of the materials in thefurnace charge. The process ensures achieving the desired chemicalanalysis of the manganese-silicon alloy end product, and particularly amanganese-silicide alloy of low carbon content, such as .05% maximum,and results in the recovery of more of the principal elements, such asabout an recovery of manganese and about recovery of silicon whichindicates that all of the silicon introduced with the charge is employedfor alloying purposes. Moreover, though the criticality of the furnaceoperation is substantially reduced, the production of a first qualityproduct having a controlled silicon content of about 28% to 32% isachieved with a minimum of operating personnel, and without the need forauxiliary equipment.

Another advantage of the process includes improved recovery of manganeseand silicon with a relatively low carbon content in the alloy, due, inpart, to improved recovery of manganese from the ore and a suitableusage of high silicon containing material, such as silicon metal.Moreover, the process can be emplo'yed with manganese ore containing avery high percentage of fines, and yet which reduces gas blowings anderuptions to a minimum.

BRIEF DESCRIPTION OF THE DRAWINGS The figure is a schematicrepresentative of the process for the production of manganese-siliconalloys, such as manganese-silicides, in accordance with the presentinvention.

DESCRJIPTION OF THE PREFERRED EMBODIMENTS In accordance with thepreferred form of the present invention, the charge for introductioninto the furnace includes a manganese ore having a predeterminedmanganese-to-iron ratio and a predetermined manganese-tophosphorusratio, and a manganese-silicon material having a substantial metallicsilicon value. The charge is introduced into the furnace with sufiicientcarbonaceous reductant to provide a melt alloy containing high values ofelemental manganese and silicon and a manganese slag. Preferably, themelt is introduced into a ladle and after a predetermined holding timethe alloy and slag are separated from one another in the ladle. In theinvention, the manganese-silicon materials preferably include metallicsilicon, a manganese-silicon alloy and a manganese-silicon slag. In theinvention, the slag is removed from the ladle and may be continuouslyrecycled having predetermined slag to alloy ratio (i.e. in the furnace)for reduction in the furnace. The molten alloy and slag removed from theladle may then be subjected to subsequent cooling, crushing and/orconcentrating operations for storage, shipping and/or for recycling tothe furnace, as will be more fully described hereinafter.

By the foregoing process, there is provided an end product having about218% to 32% silicon, 60% to 67% manganese, .05% phosphorous maximum, .05carbon maximum with the balance being substantially iron plusimpurities. In addition, the process provides a throwaway slag having acontrolled manganese content, such as 4% to 6% MnO, which may becontinuously recycled for reduction with the charge in the furnace.

The manganese ore of the type preferred for use in the present processis one that has a high manganese content and a high ratio ofmanganese-to-iron and a still higher ratio of manganese-to-phosphorous.It has been found that a preferred ratio of manganese-to-iron in the oreis about 30:1 and the manganese-to-phosphorous is about 1000zl.Moreover, it will be understood that other types of manganese ore may beutilized dependant upon the manganese and phosphorous content in theore, as aforesaid. The maximum content of the iron in the charge isdependent upon the final alloy specification. In the invention, sincethe manganese and silicon content of the alloy is about 95%, the ironcontent (plus other impurities) in the charge specifically would notexceed about 100 lbs/net ton of alloy.

Preferably, the neductant for the charge is in the form of a bulky,carbonaceous material which is employed to supply a substantial portionof the carbon reductant in the process. Preferably, a carbonaceousmaterial, such as low volatiles coal, may be employed. It is to beunderstood, however, that other reductants which may be employed in thesmelting operations may include metallurgical coke, and the like.

Now in accordance with the invention, a high silicon content material isemployed with the charge for introduction into the furnace. Preferably,such material includes metallic silicon having a silicon content ofabout 90%. The iron content of the silicon metal tobe employed in theprocess will depend upon the iron content in the manganese ore.Preferably, the iron content is less than 10% by weight and has a sizeless than about 2 inches.

In the invention, if the slag constituents in the manganese ore are toolow so as not to provide the proper slag/alloy volume ratio, it ispreferred that a throw-away manganese-silicon slag be continuouslyrecycled with the next batch to the furnach. For example, the slagproduced from the first tap may be used in the preparation of the slagrequirements of the second tap, third tap, etc. Preferably, the amountof slag in each batch should be suflicient to yield the desired slag toalloy ratio in the furnace.

In accordance with the invention, a suitable open-arc electrical furnacemay be employed which employs a three-phase electrical power source with35-inch prebatked carbon electrodes. The average spacing between theelectrodes (face-to face) is about 41 inches, with the shell of thefurnace being stationary and of a generally triangular, in top plan,construction. The inside diameter of the shell is about 23 feet and thedistance from the top of the shell to the hearth is 72 inches. Thefurnace is preferably equipped with a 10,000 lrva. transformer and mayemploy a secondary voltage (phase-to-phase) of 135 volts for thesmelting operation. In such case, the secondary current is 40,000amperes with the calculated density of the electrodes being 41.5 amperesper square inch. The charge in the furnace is preferably heated tobetween about 2500 F. to 2800" F. for between about 1 to 2 hours, andpreferably about 1 /2 hours. In the invention, though the operation hasbeen illustrated as being carried out in an electric furnace, it will beunderstood that other types of furnaces, such as induction furnaces maybe employed.

In the invention, a Chilean manganese ore may be employed in which themanganese is in the form of MnO,, and Mn O During the smeltingoperation, these higher oxides are decomposed to the lower oxide MnO. Inorder to obviate a violent decomposition of such higher oxides in themanganese ore and to prevent gas eruptions, the electrical power loadmay be lowered during the first half hour of smelting time.

In the invention, the furnace preferably includes a bottom-side tappinghole. After suflicient smelting time has elapsed, a slag is produced onthe top of the alloy. The alloy and the slag are then tapped from thebottomside opening of the furnace at about 2600 F. into a suitableladle. The alloy tapped from the bottom of the furnace containsmanganese-silicide together with silicon carbide.

In order to provide for good separation of the silicon carbide from themolten alloy, the manganesesilicide and silicon carbide mixture andmanganese silicide slag are tapped from the furnace and allowed tocooled for a predetermined time, such as 40 minutes to 60 minutes, inthe ladle until good separation occurs. The silicon carbide, beinglighter, rises to the top of the ladle, whereupon, themanganese-silicide alloy may then be removed from the ladle andbottom-side tapped into a second ladle. From the second ladle, themanganese-silicide alloy may then be top-poured into a suitablecontainer, such as a mold, for casting to the desired shape. After thecasting operation, the material may be cooled, then crushed and shippedand/or stored for shipment.

The slag remaining in the first ladle may then be poured off into ametal pot, such as cast iron. The slag may then be dumped from the pots,cooled and then subjected to a crushing operation. Certain portions ofthe dumped and cooled slag may be disposed of as waste slag while otherlarge size portions of the crushed slag containing manganese values, maythen be recycled to maintain a molten pool in the furnace. Certain otherportions of the crushed slag may be delivered to a concentrating plan torecover manganese and silicon concentrates Which, in turn, may berecycled with the charge to the furnace. In addition, certain portionsof the slag remaining after the concentrating operation may bedischarged in the form of waste slag.

In the slagging operation, if the slag constituents in the initialmanganese ore are to low in order to provide a proper slag/alloy volumeratio, some of the throw-away manganese-silicide slag from the crushingoperation is preferably recycled with the charge to the furnace. It hasbeen found that the recycling of a portion of the throwaway slag to thefurnace renders the smelting conditions in the furnace smoother andprevents overheating of the alloy. Recycling of the manganese-siliconconcentrates from the concentrating plant back to the furnace improvesthe manganese and silicon recoveries of the process.

The following examples show the chemical analysis of the charge, thesize of the charge ingredients and the analysis of the alloy productproduced in accordance with the present invention.

EXAMPLE I An open are electric furnace was charged with a mix having thefollowing composition by weight:

Chilean manganese ore: 12,180 lbs., 50% Olga coal: 4,050 lbs., 17%

Silicon metal: 2,485 lbs., 10%

Mn, Si slag: 5,600 lbs., 23%

The analysis of the above raw materials was:

Chilean ore The size of the raw materials charged into the furnace was:

Chilean manganese ore 2" x D Olga coal 1" x D Silicon metal 1" x D Mn,Si slag 3" x D The furnace was of the kind described heretofore. Asecondary voltage, phase-to-phase, of 135 volts was used with thesecondary current of 40,000 amperes and a calculated current density inthe electrodes of 41.5 A./sq. inch. The smelting time was about 2 hours.At a power load of 8,125 kw., a total of 15,600 kwh. was consumed.

The final alloy weighed 7,630 lbs. and had the following analysis:

Percent Mn 64.24 Si 30.69 C .040 P .045 Fe Balance The slag contained 6%MnO and 37% SiO The calculated recovery of manganese, disregarding anymoisture content of the manganese ore, in the aforesaid alloy was86.34%. The calculated recovery of silicon was 101.2%. The alloy washeld in the ladle for about 45 minutes to separate it from the siliconcarbide. The alloy was then removed by being bottom tapped into a secondladle from which it was top poured into a cast iron mold.

EXAMPLE II Test heats were run using the charge materials of Example Iexcept that about 50% by weight of the manganese ore and 50% by weightof the silicon metal were replaced by an alloy containing about 66%manganese and 25% silicon.

In accordance with such modification, the mix charged to the electricfurnace was as follows:

Chilean manganese ore: 5,000 lbs., 29%

Mn, Si alloy (66% Mn, 25% Si): 5,0001bs., 29% Olga coal: 1,650 lbs.,Silicon metal: 1,350 lbs., 8%

Mn, Si throw-away slag: 4,000 lbs., 24%

The analyses and the size of the mix components were similar to thoseindicated in the first example. The furnace used and the operationsperformed were also identical to those in the first example.

The weight of the final alloy was 8,200 lbs. The analysls was asfollows:

Percent Mn 63.53 Si 29.20 C .041 Fe Balance The final slag contained6.3% MnO and 35.84% SiO' and the power consumption for the total heatwas 13,500 kwh. The calculated manganese recovery, disregarding anymoisture content of the manganese ore, was 92.52% and silicon recoverywas 95.37%. The advantage of the variation of Example II is that higherproduction rates and lower consumption of silicon metal per unit of thefinal alloy were obtained.

In the invention, it is to be recognized that the carbon content of thealloy increases as the silicon content of the alloy decreases.Accordingly, the minimum tolerable silicon content of the alloy dependson the carbon specification of the alloy. For example, a carbon contentof 0.05% maximum would require a silicon content of about 28%. If thesilicon content of the alloy is too low, the carbon content would exceedthe limits specified. If the silicon content is too high, any increasein silicon beyond 32% of the designated limit would decrease themanganese content, such as below a 63% minimum, for example. Further, ithas been found that manganese silicide having an excess of 32% silicontends to disintegrate. Moreover, in the invention the silicon content inthe manganese silicide should be in the range between 28% to 32% withthe preferred amount being about 30%.

Based on the weight of the manganese ore in the charge, the reductant isadded in a weight ratio of about 1:3, the silicon metal about 1:5, andthe manganese-silicon slag about 1:2 with the weight of the chargevarying plus or minus about 5%. Where the manganese-silicon alloy isemployed with the charge, the weight ratio of manganesesilicon alloy isabout 1:1, the reductant about 1:3, silicon metal about 1:4, and themanganese-silicon slag about 0.8:1.

In the invention, the amount of recycled slag in each batch should besufficient to yield a proper final slag to alloy ratio. In Example I,the recycled slag was 1468 pounds per net ton of alloy to yield a finalslag to alloy ratio of 1.06:1; and in Example II, the amount of recycledslag was 976 pounds per net ton of alloy to yield a final slag to alloyratio of 0.6:1. Perferably, the ratios 30; the final slag and alloyshould be about 1:1 and In the invention, it has been found that aproper slag to alloy ratio in the furnace improves the heat transfer inthe charged materials and makes the smelting conditions in the furnacesmoother. In addition, the slag acts as a protective cover over thealloy, prevents overheating of the alloy and, minimizes the manganeseloss as a vapor. By the use of the preferred embodiment, recovery ofmanganese in the final alloy is about and the recovery of silicon isabout 100%. Thus, all the silicon introduced with silicon metal is beingused for alloying.

OPERATION In a typical operation and with reference to the schematicillustration, there is illustrated a preferred form for carrying out theprocess of the present invention. As shown, a charge is providedcontaining manganese ore, as at 2, containing about 60% MnO; a highsilicon bearing material, as at 4, having a silicon content of about anda manganese-silicon slag, as at 8. containing 5% MnO with a suitablereductant, as at 6, such as coal in an amount sufficient to provide amelt of manganesesilicide alloy and a throw-away slag containing about4% to 6% MnO. After the proper proportions of the charge have beenweighed, as at 10, they are mixed together and delivered to an electricopen arc furnace, as at 12, for smelting for reduction of the manganeseore by the reaction with the carbon of the reductant. During thesmelting operation, the manganese combines with the silicon metal toproduce molten manganese-silicide. The melt may then be tapped into aladle, as at 14, wherein it is allowed to cool for a time suflicient toenable the slag and silicon carbides to float to the top. Themanganesesilicide is then removed by bottom-side tapping from the ladle14 into a second ladle, as at 16, from which it is subsequentlytop-poured into a mold, as at 18, for casting to the desired shape. Thecasting may then be cooled and crushed for shipment and/or for storageand subsequent shipment, as at 20, as desired.

The slag materials produced in the first ladle, as at 14, may then bedelivered to a pot, as at 22, of cast iron or the like. From the pot 22the slag may then be dumped and cooled, as at 24. The cooled slag may besubjected to a crushing operation, as at 28, where the slag is reducedto 3-inch size and over for recycling, as at 30, back to the furnace tomaintain a molten pool therein. Dependant upon the manganese content ofthe ore, about one-third of the total large size slag produced may berecycled to the furnace. The remaining oversize slag may then be sent toa concentrating plant, as at 32, where the slag is crushed to inch sizeand down. In the concentrating steps, the metallic portion of themanganese-silicon slag is mechanically separated and recycled, as at 36,back for use with the charge in the furnace, and the non-metallicportion delivered to waste, as at 34.

In the invention, and as illustrated in Example II, it has been foundthat certain portions of the manganese ore and silicon metal may bereplaced and blended with a manganese-silicon alloy. For example, it hasbeen found that about 50% of the manganese ore and 50% of the siliconmetal may be replaced with an alloy containing manganese and silicon.For example, it has been found that an alloy containing about 64% to 68%manganese and about 25% silicon may be added to the charge with reducedamounts of ore and silicon metal. The advantages of this form are highproduction rates and lower consumption of silicon metal per unit of thefinal alloy. The manganese-silicon alloy may be prepared in the samefurnace or in a different (i.e. submerged electrode) furnace, bysmelting ore, quartzite and reductant and then remelted with themanganese ore and silicon metal in accordance with the presentinvention.

We claim:

1. A process for the production of an alloy of manganese silicidecontaining by weight about 60% to 67% manganese, about 28% to 32%silicon, a maximum of .05% carbon, a maximum of .05% phosphorus, and thebalance essentially iron which comprises,

smelting in an open hearth electric furnace, a mixture of a manganeseore, a carbonaceous reducing agent, silicon metal and a manganesesilicide slag containing 4' to 6% MnO by weight for a suificient lengthof time to form an alloy of molten manganese silicide and a manganesesilicide slag montaining 4% to 6% MnO by weight, transferring the meltto a ladle, removing the molten alloy and the slag separately from theladle, cooling and crushing the alloy, cooling and crushing the slag,and using a portion of the slag in a subsequent similar meltingoperation. 2. A process according to claim 1, wherein the manganese orehas a manganese to iron ratio of about 30 to 1. 3. A process accordingto claim 1, wherein the manganese ore has a manganese to phosphorusratio of 1000 to l. 4. A process according to claim 1, wherein thesilicon metal has about 90% silicon and is present in the charge in theratio range between 1:4 to 1:5 based upon the weight of the manganeseore. 5. A process according to claim 1, wherein the alloy when tappedfrom the furnace is held in a ladle for a suilicient length of time toobtain a separation of silicon carbide from the alloy after which thealloy is bottom-side tapped into a second ladle from which the alloy ispoured into a mold. 6. A process according to claim 1, wherein the oreis Chilean manganese ore, and wherein the carbonaceous reducing agent isOlga coal. 7. A process according to claim 1, wherein the ingredients ofsaid mixture by weight comprise about 50% ore, about 17% reducing agent,about 10% silicon metal and about 23% slag. 8. A process according toclaim 1, wherein about 50% by weight of the manganese ore and about 50%by weight of the silicon metal are replaced with an alloy containingabout 64% to 68% by weight of manganese and about 23% to about 27% byweight of silicon. 9. A process according to claim 1, wherein the slagis present in the charge in the ratio range between about O.5:1 to aboutlzbased on the weight of said manganese ore.

References Cited UNITED STATES PATENTS 2,775,518 12/1956 Udy 113,083,092 3/1963 Kuhlmann 75l33.5 X 3,329,597 7/1967 Deadrick 7580 X3,369,887 2/1968 Keyser et al. 75--l0 R 3,138,455 6/1964 Carosella etal. 75l33.5 3,395,011 7/1968 Dery et al. 7524 WINSTON A. DOUGLAS,Primary Examiner M. J. ANDREWS, Assistant Examiner US. Cl. X.R.

